This invention relates to a mine support crib column for supporting the roof of a mine.
For decades wooden cribs have been used to support the roof in mines. Typically the wood cribs are 8".times.8" and 2' to 8' high. These cribs are stacked vertically to form column supports. Such cribs are usually between 40-100 pounds each in weight, and are typically cut from lodge-pole pine or oak.
Normally, wood cribs are transported by vehicle as far into the mine as possible. They are then carried by hand to their destination, which is, of course, very labor intensive. This is due to the fact that 24 wood cribs are needed to stack an 8 foot high column.
Another problem with wood cribs is that the cribs are not tied together. When a roof moves or shifts relative to the floor, a wood crib column cannot sustain non-lateral movement. The top cribs begin to roll and the column begins to fail.
A wooden crib's ultimate load bearing capacity can be significantly affected by the localized behavior of one timber within a crib. For example, if one wood crib has rotten timber or is taken from a weak part of the tree, it is in the weakest part of the column. The entire column is only as strong as the one weak crib. The compressive properties of wood are also dependent upon the wood's moisture content and grain orientation.
It is therefore an objective of this invention to provide a roof support column structure that will sustain lateral shifts in the roof and is of uniform construction.
As wood cribs become more scarce, the need for an alternative becomes a necessity. Such an alternative should insure an endless supply of support materials superior to that of wood, and at prices competitive to wood even before installation and transportation costs are considered.
An alternative to wooden cribs should be lighter in weight and easier to handle than conventional wooden cribs. Such an alternative should have the added advantage of being rollable when necessary to install in remote locations in the mine.